1. Field of the Invention
The invention relates to a circuit apparatus, and more particularly to a circuit apparatus having a low-voltage device that is operable under a high voltage source.
2. Description of the Related Art
With the development of the semiconductor manufacturing processes, the density of transistors on a chip or die is getting higher and higher. However, the operation voltage of the chip is getting lower and lower. If a chip, which is manufactured by so-called the 0.13-micron CMOS (Complementary Metal Oxide Semiconductor) process and the operation voltage can be as high as 1.2 volts, operates under the voltage of 3.3 volts, the chip will be damaged in a few seconds due to the 3.3 volts, which is the conventional operation voltage, exceeds the breakdown voltage of the chip formed by the 0.13-micron process. However, several chips are formed on a circuit board, so a commonly specified output amplitude has to be reached in order to communicate data among these chips. As for the digital signal, the usual output amplitude is 3.3 volts. In order to make the output amplitude of the signal reach 3.3 volts, the manufacturer usually provides one or more devices, of which the operation voltage is 3.3 volts, for input/output circuits. The device, which may resist 3.3 volts, has a gate insulation layer having a thickness almost the same as that of a device manufactured using the 0.35-micron CMOS process.
In the aspect of the analog communication, the analog communication protocol is usually provided for the long-distance signal transmitting and receiving. For example, the analog communication protocol may be used for the information interchange between two computers. Since the analog communication protocol is used in the long-distance signal transmitting and receiving, it is necessary to consider that the signal may be influenced and attenuated owing to the wire or cable. Consequently, these communication specifications require a greater output amplitude such as 2 volts. If the advanced process, such as 0.13-micron process, is to be used to manufacture the analog communication circuit, the devices that operate under the voltage of 3.3 volts. Since the device, which can operate at 3.3 volts, has a gate insulation layer having a thickness almost the same as that of a device manufactured using the 0.35-micron CMOS process, its operation speed is much slower than the device that operate at 1.2 volts.
Therefore, the chips usually must have two kinds of devices that may have two different operation voltages, respectively. One kind of the devices may have a low operation voltage and a high operation speed, while the other kind of devices may have a high operation voltage and has a low operation speed. Therefore, it is problematic to design an analog circuit that may have a high operation voltage while having a high operation speed.